the earth’s atmosphere. what holds the earth’s atmosphere to the planet? gravity
TRANSCRIPT
Development of the Earth’s Atmosphere
• Primordial atmosphere (4.6 to 4.0 bya)
• Evolutionary atmosphere (4.0 to 3.3 bya)
• The living atmosphere (3.3 bya to 500 mya)
• The modern atmosphere (500 mya to present)
The Modern Atmosphere (500 mya to the present)
• Nitrogen, N2 (78%)
• Oxygen, O2 (21%) 99.9%
• Argon, Ar (0.9%)Trace gases
– water vapor (0-4%)– carbon dioxide (.036%), methane (greenhouse
gases)– nitrogen oxides, sulfur oxides (acid rain and
more)– many other trace gases– particulate (dust)
Atmospheric PressurePressure can be thought of as
the weight of all overlying air (though, in reality, pressure exerts force in all directions).
Mercury Barometer- Invented by Toricelli, 1643
Average Sea Level Atmospheric Pressure:
29.92” of Mercury76 cm of Mercury1013 millibars (mb)
Aneroid Barometer- also altimeter
Average Sea Level Atmospheric Pressure:
29.92” of Mercury76 cm of Mercury1013 millibars (mb)
Atmospheric Pressure Is Related to Weather
ConditionsLess-Dense, Low
Pressure Rises: Clouds and Stormy Weather
More-Dense, High Pressure Air Sinks: Fair Weather
Temperature, Precipitation, and ElevationTemperature decreases with increasing elevation.
Precipitation increases with increasing elevation.
Temperature InversionsWhen warmer air overlies cooler air, pollutants and fog are trapped beneath the inversion.
Common Winter Radiation Inversion in Valleys
Troposphere[tropopause at 8-18 km, or 5-11 miles]
• Troposphere– contains 90% of the mass
of the atmosphere – decrease of mass with altitude– mostly mixed gases (not
layered)– clouds / weather layer– temperatures decrease with
altitude - WHY?
Stratosphere
– decrease in amount of gases with altitude
– mixed gases (not stratified) except for ozone layer
– temperatures increase with altitude
[stratopause at 50 km, about 30 miles]
[tropopause at 8-18 km, or 5-11 miles]
mesosphere
Aurora borealis / australis• The northern / southern lights
(click for video)• (click for photos and legends)
• Thermosphere and uppermost Mesosphere– solar wind (clouds of electrically charged
particles)– Earth’s magnetic field directs them towards
poles
– excite oxygen (O) and nitrogen (N2) ions in ionosphere emit light
• Ozone forms naturally in stratosphere
• UV radiation (sun) --> mutations– plankton reduced (food chain base), crops
decline– weaker immune systems, skin cancer
• Stratospheric ozone (O3) absorbs UV rays
The Importance of Stratospheric Ozone
O2 2 O then O + O2 O3
light
O3 O2 + O
UV rays
The Importance of Stratospheric Ozone
CFC’s– link to ozone hole established in 1970s– Chloroflourocarbons (refrigerants,
aerosols)– one Cl can decompose more than 100,000
O3
– Montreal Protocol, 1987: U.N. agreement on ban
– up to 10 years for rising CFC gases to reach stratosphere; once in the stratosphere, CFC’s can last up to 50-100 years